The Pope, formerly cardinal Jorge Mario Bergoglio, appeared from a window of the papal apartment where he then asked for his followers to pray for him.

"Thank you for your welcome and for your prayers," he said.

Dozens of flags from Francis's native Argentina were waving among the crowd, along with flags from other Latin American nations including Colombia, Peru, Paraguay and Mexico.

One banner read: "Francis, you are the springtime of the church", reflecting a groundswell of hope that the choice of a humble outsider has inspired in many Catholics weary of Vatican scandal and dysfunction.

Traditionally, a pontiff's first Angelus prayer has been a moment to comment on international issues, but Francis instead used the occasion to emphasise his Italian roots.

The Argentine, whose parents hailed from Italy's north-western Piedmont region, said he chose to name himself after St Francis of Assisi because of his "spiritual ties with this land".

Earlier, in another sign of his impromptu and humble approach to the papacy, Francis conducted a private mass for Vatican City residents and greeted crowds waiting for him outside a small church.

He grabbed an opportunity to shake hands with well-wishers, plunging into crowds pushing against barricades outside a Vatican gate as security men and Swiss Guards stood nervously by.

Chanting "Viva Il Papa" and calling his name, the well-wishers jostled to greet the first Latin American pontiff.

The 76-year-old pope's informal style is markedly different from that of his more austere 85-year-old predecessor Benedict XVI, who stunned the world last month in announcing his resignation due to his advanced age.

World leaders who will be among the million people expected to attend the Pope's inauguration mass on Tuesday have begun to fly into Rome.

One of them is Argentine president Cristina Kirchner who had tense relations with the former archbishop of Buenos Aires before his elevation to pope.